/Engine/Source/Runtime/GeometryCore/Public/Generators/StairGenerator.h
All UVs for a given side are shared except for Front & Top. Border edges along each side are UV island edges.
FVector2f GenerateUV ( [ESide](API\Runtime\GeometryCore\Generators\FStairGenerator\ESide) Side, int Step, int VertexId, float UVScale )